Fill in the blank by using the correct future tense.
Don't worry ________ late tonight.

The correct answer is Option A (if I am).

Key Points:
• Concept: Subordinate clauses of condition/time referring to future time. In conditional clauses introduced by 'if' or time clauses introduced by 'when', the Present Simple Tense is used instead of Future Tense ('will').
• Explanation: 'Don't worry if I am late tonight' expresses a possibility. We use 'if + Present Simple' ('if I am') to talk about a potential future scenario.
• Other Options: 'if I'll be' incorrectly uses future tense in a conditional clause. 'when I am' implies certainty rather than a conditional possibility.
• Official Key: Option 1 ('if I am') is the official correct answer.
• Key Takeaway: Remember: Never use 'will' inside an 'if' conditional clause; use simple present instead.